Centrifugation is often employed for separating suspended cells and other particulates from a liquid component. Examples of fields which employ centrifugation in this manner include cellular biology, hematology, cellular diagnostics, and cellular therapy. During centrifugation, the cellular component sediments and forms a pellet at the centrifugal end of the container. Meanwhile, the liquid component forms a liquid supernatant above the pellet. After the pelleting process has been completed, the supernatant is decanted from the container, taking care to leave the pellet behind.
The initial separation step may be followed by one or more wash steps. During each wash step, the cellular component is resuspended in a wash liquid. The resuspended cellular component is then pelleted once again by means of centrifugation. The supernatant wash liquid is then decanted from the container, taking care once again to leave the washed pellet behind. If a particularly thorough wash is desired, the pelleted cellular component may be repeatedly washed in a serial fashion by means of this protocol.
The wash steps may be followed by one or more chemistry steps. During a chemistry step the washed cells may be treated with a reagent which reacts with the cells or a subpopulation of the cells. The cells may be chemically labelled by the reagent or may be otherwise chemically modified or treated. For example, labelled antibodies may be employed to bind to cells having specific surface antigens. Cells lacking the specific surface antigen remain unlabelled. After the chemistry step, unreacted reagent may be separated from the cellular component by means of further wash steps, similar in protocol to the earlier wash steps, each employing centrifugation and decantation.
Pioneer workers in cellular biology and related fields were required to performed several steps of the wash cycle in a manual fashion, viz. removing the centrifuge tubes from the centrifuge rotor after the initial pelleting; decanting the supernatant liquid from the centrifuge tubes; adding wash liquid to the pellet; re-suspending the pellet within the wash liquid; and remounting the centrifuge tubes back onto the centrifuge rotor for further pelleting. These manual operations can be laborious and tedious. Such tedium can lead to technician error.
Special centrifuge rotors have been developed for eliminating much of this tedium. Such centrifuge rotors have been designed to load and unload liquids directly to and from centrifuge tubes which remain mounted on a centrifuge rotor. Fleming et al. (U.S. Pat. No. 3,951,334) and Weyant, Jr. (U.S. Pat. No. 4,431,423) disclose a centrifuge from which liquid may be decanted without unmounting the centrifuge tubes. Intengan (U.S. Pat. No. 4,285,463) discloses a centrifuge from which liquid may be decanted and into which liquids may be dispensed without unmounting the centrifuge tubes from the centrifuge rotor.
Each of the above devices employs centrifugal draining to decant liquid from the centrifuge tube. During centrifugal draining, the centrifuge tube is held at a negative angle with respect to the vertical such that the bottom of the centrifuge tube is closer to the axis of the rotor than the top of the centrifuge tube. The centrifuge rotor is then spun while the centrifuge tubes are held at this negative angle. The rotational speed of the centrifuge is sufficient to drive the liquid from the centrifuge tube by means of centrifugal force.
Unfortunately, centrifugal draining can result in aerosol formation within the bowl of the centrifuge. After the liquid leaves the centrifuge tube, it may splash at high velocity against the wall of the bowl. The resulting aerosol may be difficult to contain and, if the cellular samples are biohazardous, the uncontained aerosol may dangerously contaminate the work place.
Centrifugal draining can also result in the loss of pellet material. Unless the cellular component forms a tight pellet at the bottom of the centrifuge tube, centrifugal draining can drive the cellular component out of the centrifuge tube with the liquid component. Hence, the utility of centrifugal draining may be limited to the separation of cellular components which pellet tightly or for which a partial loss of the cellular component is acceptable.
What is needed is a centrifuge which can dispense liquids directly into centrifuge tubes, which can spin such liquids so as to form a pellet, and which can automatically decant such liquids from the centrifuge tubes with little or no aerosol formation and/or with little or no loss of pellet material.